Buying resale apartment before posession

Guys I need some urgent advice. I am in process of buying a resale apartment, and have some issues with the process suggested by the seller. The seller suggests:

1) We sign an MOU.2) Seller gets a foreclosure letter in his name.3) I pay off seller loan.4) Wait for orginal papers are recieved for bank by the seller (bank would only release the documents to the seller).5) We sign tripartite agreement with builder and pay the rest of amount to seller.

My problem is what if I pay off loan, and seller than gets the papers, take posession.

What I am suggesting is (but the seller is not agreeing too)1) We sign an MOU.2) Seller gets the foreclosure document from bank.3) We sign the tripartite agreement, where I pay builder dues, and loan amount ( about 50% of total transaction amount). The agreement states that it requires the bank copy of agreement to be valid.4) Seller getsh the original documents.5) I and Seller exchange the documents and balance payments.

Can people comment on what the common practices are for such a situation. I really need to resolve this urgently, and any inputs would be most welcome.